Crazy hesitation under 3000RPMS/LEAN

[gdanski_z]

After I got my car back together from the winter, I have been chasing some minor problems. I have cleared up all the minor issues, and I am still stuck scratching my head on the major issue I have. While revving the engine in Neutral, or under load, my 300zx TT hesitates anywhere under 3000RPMS. After I hit 3000RPMS the car is smooth as silk. I changed both O2 sensors after noticing the readings coming from my bank 1 O2 sensor. At this point, it seemed to fix the problem for about 30 minutes, but came back again. Now heres the odd part...If i drive the car without the right O2 sensor plugged in, it funs flawlessly, smooth throughout every gear and every aspect of acceleration, BUT...during this time the car runs EXTREMELY rich. With the O2 unplugged the car runs around 13.7 at idle, but while cruising at normal throttle it runs 17's and higher on my A/F ratio gauge. The drivability of the car when the O2's are plugged in with the hesitation is terrible, and seems to get worse the longer I drive.

Things I have checked for this issue:
-Coil packs
-MAF sensor
-Boost leaks
-vacuum leaks (smoke test)
-changed both O2's

The only thing that I can think may be a cause is my BOV's. Under load I can hear a noise as if air is entering the system through my BOV. It is a loud air sucking noise in which I did not have before. I was thinking of a possible leaking BOV that is letting in unmetered air on bank 1, the bank that I'm having issues with.

Any input would be appreciated.

[bentotdagr3at]

check your timing. mine was kinda hesitating a little bit and found out that i was only running 7.5 degrees on my timing. adjusted the cas and now i'm running 15 degrees and seems to be a lot smoother. although i'm still in safety boost i think.

[ZL8NING]

Read the codes and see what you've got. It might be the detonation sensor causing safety mode....

[gdanski_z]

Code 55 all good there...Car barely runs on cold start unless i hold the gas pedal down and give it gas..once it warms up its ok, idles good and at around 13.8 on my A/F gauge. Runs not that bad for the first few minutes and then it misfires anywhere under 3000RPMS in any gear. On the highway if I give it some gas it hesitates and misfires so hard that it shakes the whole car like crazy and goes LEAN when its missing. Adjusted the throttle body screws because one side was opening before the other and they weren't synced...that helped my extremely lean issue....now it only goes lean if it misfires. Sometimes at idle it will run smooth as silk, and then the misfire would kick in for 10-15 seconds and then kicks back to smooth again...ready to rip my hair out

[amiry36]

What kind of spark plugs are you running?

[amiry36]

Your spark plug gap could be off which causes random misfires at lower RPM.

[gdanski_z]

Ngk r bkr7e

[emiliog2276]

Ngk r bkr7e

These Z's are picky when it comes to spark plugs.

PFR6B-11B would be the TT stock plug .

[gdanski_z]

Ngk r bkr7e

These Z's are picky when it comes to spark plugs.

PFR6B-11B would be the TT stock plug .

I'm not stock though... These were the plugs my tuner put in last year, and I've run them since.

[amiry36]

I had same misfire problems because i was running iridiums. Switched to ngk platinums and it was running good.

Anyways, check your spark plug gap. Tell us what it is.

[emiliog2276]

Plug Gap Settings:

0.044" - Stock
0.035" - 15psi
0.031" - 18psi

[emiliog2276]

I was just adding onto the plugs info. But I have pretty much the same exact problem. Except unplugging the O2 does nothing (ive replaced them and the connectors on the wiring harness) . But there can be so many reasons ive learn to live with it for the time being.

http://www.premierz.com/300zx-hesitation/

If your car is hesitating badly when warm. If you turn the car off and turn it back on again does the hesitation disappear briefly?

[amiry36]

Check your tps. Fill it with 91 octane or higher gas. Many hesitations come from poor quality gas. Ohm test your injectors and ohm test your ECU coolant temperature. Coolant temp sensor is known to do weird stuff. Check your timing with the light.